Swiss drugmaker Roche faces the prospect of hiring an outsider to replace its chairman of 16 years after its most suitable board members turned down the job. The 117-year old company - the world's largest maker of cancer drugs - set itself an autumn deadline to find a successor to Franz Humer, an influential, hands-on former Roche chief executive who says he will not stand for re-election next year. But the search hit an early stumbling block when the CEOs of Shell and Nestle, who both sit on Roche's board, said they weren't interested.